Contact structure for a vacuum-type circuit interrupter



May 22, 196 A. N. GREENWOOD CONTACT STRUCTURE FOR A VACUUM-TYPE CIRCUITINTERRUPTER Filed May 11, 1959 Inventor: Allan N. Greenwood by 52am HisAttorn e5.

3,036,180 CONTACT STRUCTURE FOR A VACUUM-TYPE CIRCUIT INTERRUPTER AllanN. Greenwood, Havertown, Pa., assignor to General Electric Company, acorporation of New York Filed May 11, 1959, Ser. No. 812,195 12 Claims.(Cl. 200-144) This invention relates to a vacuum type circuitinterrupter and, more particularly, to contact structure for such aninterrupter.

The usual non-vacuum-type circuit interrupter comprises a pair ofseparable contacts, one of which is movable through an opening andclosing stroke and the other of which is generally fixed. It iscustomary in such interrupters to provide the generally fixed contactwith a limited degree of resilience so as to reduce the mechanicalshocks occurring when the contacts are driven into engagement duringclosing and so as to reduce the tendency of the contacts to bounce uponbeing driven into closing engagement. In addition, this resilienceenables a predetermined pressure to be maintained between the contactswhen the interrupter is closed and also provides a wear allowance toaccommodate erosion of the contacts.

The above advantages are equally desirable in a vacuum-type circuitinterrupter but heretofore have been difficult to attain for severaldifferent reasons. One reason arises out of the fact that a vacuum-typecircuit interrupter must be baked out before it can be relied upon forsatisfactory performance. This bake-out procedure involves baking theinterrupter at relatively high temperatures in order to remove anyadsorbed gases from the internal surfaces of the interrupter so as toavoid subsequent impairment of the vacuum inside the interrupter whenthe interrupter is in service. The high temperatures accompanying thebake-out are such that the resilient properties of any conventionalspring, e.g., a coil or leaf spring made of a conventional resilientmaterial, located inside the interrupter would be seriously impaired, ifnot completely destroyed, by the bake-out. Thus, such a conventionalspring cannot be relied upon for imparting the desired resilience to thefixed contacts.

Another reason that it has been difficult to attain the above-notedadvantages of a resilient mounting is that such mountings customarilyinvolve a certain degree of relative motion between theresiliently-mounted contact and its support, and such relative motioninvolves a certain amount of friction. Friction in a vacuum can be anextremely troublesome problem because the coefiicient of frictionbetween most clean metals in a vacuum is very high. This, of course, canproduce galling or virtual welding together of the two surfaces that areintended to slide relative to each other, with the end result beingcomplete impairment of the resilient mounting.

One approach that has been made toward overcoming these problemsinvolves mounting the springs and bearings for the resiliently-mountedcontact outside of the vacuum envelope. This results in an elaborate andcostly design which it is desirable to avoid if possible.

Thus, an object of my invention is to provide for one of the contacts ofa vacuum-type circuit interrupter a resilient mounting which utilizes aspring device located inside the vacuum envelope.

Another object is to construct the internally located resilient mountingin such a manner that its spring properties are not impaired by theusual bake-out of the interrupter.

Still another object is to construct the internally-located resilientmounting in such a manner that sliding motion between'its parts can takeplace without undue frictional Patented May 22, 1962 ice interferenceresulting from the presence of the vacuum inside the interrupter.

In carrying out my invention in one form, I provide within the usualvacuum chamber of the interrupter a pair of separable contacts. Onsuitable supporting struc ture within the vacuum chamber, I resilientlymount one of the contacts by means of a sealed gas-filled capsule havingflexible metallic walls which permit compression of the gas within thecapsule. The capsule is disposed between the supporting structure andthe contact in such a manner that the gas within the capsule iscompressed by closing motion of the other contact after initialcontact-engagement occurs. The compressed gas provides a force acting ina direction to resist contact-separation. Inasmuch as a gaseous mediumis relied upon for the spring properties of the resilient mounting andinasmuch as the spring properties of such gaseous medium are notpermanently affected by the temporary temperature rises accompanyingbake-out, it will be apparent that the spring properties of my resilientmounting will be retained unimpaired despite any bake-out to which theinterrupter is subjected.

In accordance with another feature of my invention, I guide the movablecontact during its motion by suitable guide means. This guide means hasits bearing surfaces located within the gas-filled capsule, instead ofin the vacuum, thus eliminating any undue frictional interference thatwould result if the sliding surfaces were located in the vacuum.

For a better understanding of my invention reference may be had to thefollowing description taken in conjunction with the accompanyingdrawing, wherein:

FIG. 1 is a side elevational view partly in section showing avacuum-type interrupter embodying one form of my invention.

FIG. 2 is an enlarged sectional view of one part of the interruptershown in FIG. 1.

FIG. 3 is a schematic showing of a slightly modified form of myinvention.

Referring now to FIG. 1, there is shown a highly evacuated envelope 10comprising a casing 11 of suitable insulating material and a pair ofmetallic end caps 12 and 13 closing off the ends of the casing. Suitableseals 14 are provided between the end caps and the casing to render theenvelope 10* vacuum-tight.

Located within the envelope 10 is a pair of separable disc-shapedcontacts 17 and 18 shown in their disengaged or open-circuit position.The upper contact 17 is a generally fixed contact mounted on astationary conductive rod 17a, which at its upper end is united to theupper end cap 12. The mounting between the upper contact 17 and theconductive rod 17a is constituted by a spring device S embodying oneform of the present invention, as will be described in greater detailhereinafter. The lower contact 18 is a movable contact joined to aconductive operating rod 18a which is suitably mounted for verticalmovement. The operating rod 18a projects through an opening in the lowerend cap 13, and a flexible metallic bellows 20 provides a seal about therod 18a to allow for vertical movement of the rod without impairing thevacuum inside the envelope 10. As shown in FIG. 1, the bellows 20 issecured by suitable seals at its respective opposite ends to theoperating rod 18a and the end cap 13.

Coupled to the lower end of the operating rod 18a, there is providedsuitable actuating means (not shown) which is capable of driving thecontact 18 upwardly into engagement with the contact 17 so as to closethe interrupter and which is also capable of returning the contact 18downwardly to its illustrated position so as to open the interrupter.These circuit-controlling operations, particularly as they involve theresilient mounting S, will soon be explained in greater detail.

Each of the disclosed contacts 17, 18 is of a disc shape and ispreferably constructed as shown and claimed in application Serial No.730,4-l3-Schneider, filed April 23, 1958, now Patent No. 2,949,520,granted August 17, 1960, and assigned to the assignee of the presentinvention. It is to be understood, however, that any suitable form ofcontact structure can be'used with the contact mounting arrangement ofmy invention.

The contact-mounting arrangements will now be described in greaterdetail, with particular reference being had to FIG. 2. Referring now toFIG. 2, it will be seen that the spring device S comprises a sealedcapsule formed from a flexible bellows 31 of tubular form and a pair ofend structures 32, 33 closing off the bellows '31 at its longitudinallyopposite ends. Each of these end structures comprises an end plate 32 tothe inner side of which is brazed a sheet metal ring 33 terminating inan axially extending flange 34 to which the end of the tubular bellows31 is welded. The brazed joint 35 between the end plate "3 2 and thering 33 and the welded joint 36 between the ring 33 and the bellows 31each form gastight seals for isolating the inside volume of the capsulefrom the surrounding volume.

The capsule 30 is filled with gas at a predetermined pressure and thisgas is relied upon for the spring properties of the contact mountingarrangement S, as will soon be apparent. The opening for filling thecapsule 30 with gas is not shown, but it is to be understood that thisopening is permanently sealed off after the capsule has been filled. r

The upper end plate '32 is secured to the stationary conductive rod 17::by suitable fastening means such as a threaded stud 38 integral with theend plate 32 and threaded into asuitably tapped hole in the rod 17a. Thelower end plate 32 of the capsule 30 issecured to the contact 17preferably by means of a threaded stud 39 integral with the lower endplate 32 and threaded into a suitably tapped hole in a centrallydisposed boss provided on the contact 17. 1

When the lower contact 18 is driven upwardly during a contact-closingstroke, it encounters the generally fixed contact 17 near the end of itsclosing stroke and then travels a short distance further in an upwarddirection until the closing stroke is completed. This continued upwardmovement of the contact 18 after initial contact-engagement forces thecontact 17 upwardly, thereby decreasing the volume of the capsule 30 andthus compressing the gas within the capsule '30. As the gas iscompressed, it, of course, acts in the same general manner as a spring,.thus cushioning the shock of the closing impact and exerting aprogressively increasing downward force tending to preclude contactbounce. The downward force exerted by the compressed gas also maintainsa predetermined desired pressure between the contacts when they areengaged and serves the additional purpose of compensating for anycontact erosion. Upward motion of the contacts 17 and :18 is terminatedwhen the lower contact 18 reaches the end of its closing stroke, andthereafter the two contacts are held in this terminal position bysuitable restraining means such as a latch (not shown);

constituting a part of the operating mechanism. The terminal point forthe opening stroke is governed by the construction of the operatingmechanism.

For guiding the generally fixed contact 17 during its above describedupward motion, guide means 40 is pro vided internallyof the gas-filledcapsule -30. The guide means 40 comprises a guide sleeve 42 integralwith the lower end cap 32 and extending upwardly therefrom and a guiderod 43 integral with the upper end cap andiextendin'g downwardlytherefrom. The guide rod 43 is slid- ,ably received in telescopingrelationship within the guide sleeve 42, and these two parts constitutea slide bearing which serves to guide the movable contact 17 along asubstantially straight line path as it mov'es'upward .under theinfiuenc'e'of closing forces applied through the movable contact 18. Asmallhole 44'provided in the guide CQl 4 sleeve 42 near its lower endprecludes gas from being trapped within the guide sleeve during suchupward movement.

For providing a stop during contact-opening movement, the guide rod 42is provided with a transversely extending pin 45 that is looselyreceived within a slot 46 formed in the guide sleeve 42. The slot 46 isof sufficient length to insure that the pin 45 does not interfere with aclosing operation, but during an opening operation the pin 45, uponengaging the upper end of slot 46, serves to limit the downward travelof the movable contact 17.

For example, when the hold-closed latch (not shown) is released and themovable contact 18 moves downwardly under the influence of its openingspring (not shown), the compressed gas within the capsule 30 forces thegenerally fixed contact 17 to follow along in follow-up relationship tothe movable contact 18. This follow-up motion continues until the pin 45reaches the upper end of the slot 46, at which time the fixed contact 17is blocked from further downward motion, thereby permitting the movablecontact 18 to separate from the fixed contact 17 and, thus, to establishthe desired circuit-interrupting are between the two contacts 17 and 18.

As was pointed out hereinabove, friction can be an extremely troublesomeproblem in a vacuum interrupter because the coefficient of frictionbetween most clean metals is very high in a vacuum. This leads togalling and welding between the two surfaces that are intended toconstitute the bearing. I have overcome this problem in mycontact-mounting arrangements by locating the guide means (40) for themovable contact inside the gasfill-ed capsule 30 instead of in thevacuum chamber. As a result, the guide means is not subject to thegalling and welding problems that would have been present had the guidemeans been located in the high vacuum of the vacuum chamber. v

For transferring current between the conductive rod 170 and the contact17, I provide flexible conductive braids 50 also located within thecapsule 30. Each of I these braids has its upper end connectedelectrically and mechanically to the guide rod 43 and its lower endconnected electrically and mechanically to the guide sleeve "42, thusproviding an electrical connection which bridges the guide means 40.Locating the braids 5f) inside the capsule 30, instead of in the vacuumchamber, is highly advantageousfor a number of reasons. ;First of all,the necessity for freeing the braids of adsorbed gases is eliminated.This can be a formidable problem in view of the fact that a braid ismade up of a large number of strands 'each having a surface which mustbe freed of adsorbed gases and, at the same time, is difficult tofree ofadsorbed gases. Secondly, flexing of the braids involves a certainamount of friction between the strands of the braid, and the vacuumwould tend to accentuate this friction due to the high coefiicient offriction prevailing between clean metal surfaces in a high vacuum.

The resulting high friction would shorten the useful life 7 of a braidin comparison to its life in most gases such as air.

It will be apparent thatmy capsule 30 is a self-contained sub-assemblythat can be easily assembled apart from the interrupter and then readilyincorporated into the interrupter. Starting with the end caps 32 havingtherings 34 brazed thereto, the sub-assembly is assembled simply by'placing the guide rod 43- of the upper end structure 32 inside the guidesleeve 42 of the lower end cap structure 32, pressing the transverse pin45 in place, attaching the braids 50, and then slipping the bellows 31overthe two end structures 32 and welding it into position. Thereafter,the capsule is filled to the desired pressure with a suitable gas andthen sealed.

This sub-assembly can then be incorporated into the vacuum interruptersimply by screwing the stud 34 into the tapped opening of the rod 17aand screwing thedisc I i 7 shaped contact 17 onto the lower stud 36.When so assembled, the upper end cap 3-2 abuts against the lower surfaceof the rod 17a thereby providing for current tansfer between the rod17:: and the end cap 32. Correspondingly, the lower end cap 32 abutsagainst the upper surface of the boss on the contact 17, therebyproviding for current transfer to the contact 17 from the lower end cap32. Suitable brazed joints such as shown at 37 are preferably providedbetween the rod 17a and the end cap 32 and between the contact 17 andthe lower end cap 32 to prevent loosening of the threads 38 and 39,thereby maintaining the desired electrical engagement between the endcaps 32 and the adjacent surfaces of the interrupter.

As was pointed out hereinabove, a vacuum switch must be baked-out athigh temperatures before it can be relied upon for satisfactoryperformance. The temperatures involved in the usual bake-out operationare so high that any conventional metallic spring or spring constructedof organic material disposed in the vacuum envelope would have itsresilient properties impaired or even destroyed by the bake-out. Incontrast to conventional metallic springs or springs of organicmaterial, the contact-mounting arrangement of my invention can besubjected to bake-out temperatures of any desired level, withinpractical limits, without in any way impairing the spring properties ofmy assembly. I am relying upon the gas within my capsule for providingthe desired spring properties, and it will be apparent, of course, thatthe propeities of this gas will not be significantly affected by thebake-out. Once the interrupter returns to normal temperatures afterbake-out, the gas within the capsule will have substantially the samespring properties as it had before bakeout. Any resilience present inthe bellows may be destroyed by the bake-out, but this is no significantdisadvantage inasmuch as I rely upon the gas within the capsule and notupon the bellows itself for providing the desired resilience. It is tobe understood that the spring gradient of my resilient capsule 30 can bepreregulated by selection of a suitable initial pressure for the gaswithin the bellows.

It is desirable to protect the bellows 31 from the effects of any arcestablished between the contacts 17 and 18. For this purpose I provide acup-shaped metallic shield 55 surrounding the bellows. This cup-shapedshield, which is shown brazed to the lower end plate 32, is preferablyincorporated into the spring sub-assembly before the sub-assembly isincorporated into the interrupter.

Although air, argon, nitrogen, and numerous other gases are suitable foruse as fillers for the capsule, there is one gas which is exceptionallywell-suited for this purpose. This gas is helium. One characteristic ofhelium that renders it highly advantageous for use in this applicationis that helium, being a monatomic gas, has a relatively high gammacoeflicient, i.e., a relatively high ratio of specific heat at constantpressure to specific heat at constant volume, as compared to the gammacoefiicient of polyatomic gases. For example, the gamma coefficient fora monatomic gas such as helium is 1.67 as compared to 1.4 for diatomicgases. This relatively high gamma coetficient renders heliumexceptionally advantageous as a filler for my capsule inasmuch as agiven decrease in volume of the capsule produces a relatively largeincrease in the pressure of the gas within the capsule. Thus, by usinghelium, a higher spring gradient can be obtained than with polyatomicgases, and this is especially advantageous where the available motion ofthe generally-fixed contact is small.

Another characteristic of helium that renders it highly advantageous foruse in this application is its high thermal conductivity. Because ofsuch high thermal conductivity, the helium can be relied upon tofacilitate heat transfer from the contact structure 17 to the upper endcap 12 via a path extending from the lower end of the capsule 30 to theupper end. In addition, the helium because of its high thermalconductivity helps to cool the parts within the bellows and to transferheat'from such parts to the upper end cap 32 at a relatively high ratein comparison to that available with most other gases. The combinationof these two properties renders helium, or a gaseous mixture containinghelium exceptionally well-suited for use as a filler for my capsule 30.

Any suitable lubricant, such as graphite, which is capable ofwithstanding the usual high bake-out temperatures without decompositioncan be used for the guide bearing 40. Because such lubricant is locatedwithin a gaseous atmosphere instead of in the vacuum, there is no dangerof any loose particles therefrom contaminating the vacuum andinterfering with circuit interruption.

Although not shown, it is to be understood that a suitablevapor-condensing shield is provided between the arcing gap and theinsulating housing 11 to protect the surfaces thereof from thedeposition of arc-liberated metallic particles thereon. For a detailedexample of such a shield, reference may be had to application S.N.630,247, Crouch, now Patent No. 2,892,911, assigned to the assignee ofthe present invention.

One type of interrupter in which my resilient mounting can be used toparticular advantage is an interrupter including a plurality of breaksconnected either in series or parallel. An interrupter of this typehaving parallel-com nected breaks is shown schematically in FIG. 3,where each of the generally stationary contacts 17 is shown mounted bymeans of a resilient mounting S corresponding to the mounting S of FIGS.1 and 2. Any desired number of such breakers with correspondingstationary contact arrangements can, of course, be utilized inside asuitable envelope. Utilizing my spring mountings S contributes to a muchsimpler overall construction than could be attained if the stationarycontacts were resiliently mounted by means of springs individual to eachstationary contact located outside the envelope. Such an external springarrangement would require a separate bellows of the type shown at 20 foreach stationary contact, and this would involve numerous complications.In the arrangement of FIG. 3, the movable contacts 18 are mounted on acommon reciprocable support 60 for moving them jointly either into orout of engagement with the contacts 17 through the movable operating rod18a. The resilient mountings S serve the various functions describedhereinabove in connection with FIGS. 1 and 2 and also serve to maintainthe desired contact pressures in spite of uneven contact-wear orerosion.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects and I, therefore, intend in theappended claims to cover all such changes and modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A vacuum-type circuit interrupter comprising means defining a vacuumchamber, a pair of separable contacts disposed within said chamber,means for moving one of said contacts into and out of engagement withthe other of said contacts comprising a movable contact actuating memberconnected to said one contact and disposed at least partially withinsaid vacuum chamber, supporting structure for said other contactdisposed within said vacuum chamber, means within said vacuum chamberfor resiliently mounting said other contact on said supporting structurecomprising a sealed gas-filled capsule having flexible metallic wallspermitting compression of the gas within said capsule, said capsulebeing disposed between said supporting structure and said other contactin such a manner that the gas within said capsule is compressed byclosing motion of said one contact after initial engagement with saidother contact, said compressed gas providing a force acting in adirection to hold said contacts in engagement, the surfaces of saidinterrupter that are exposed to the vacuum Within said vacuum chamberbeing substantially free of adsorbed gases.

2. A vacuum-type circuit interrupter comprising means defining a vacuumchamber, a pair of separable contacts disposed within said chamber andarranged for .relative movement into and out of engagement with eachother, supporting structure for one of said contacts disposed withinsaid chamber, means within said chamber for resiliently mounting saidone contact on said supporting structure comprising a sealed gas-filledcapsule having flexible metallic walls permitting compression of the gaswithin said capsule, said capsule being disposed between said supportingstructure and said one contact'in such a manner that said gas iscompressed by contact-closing motion of said contacts after initialcontact-engagement is established and acting thereafter to resistcontact separation, the surfaces of said interrupter [that are exposedto the vacuum within said vacuum chamber being substantially free ofadsorbed gases.

' 3. The vacuum-type circuit interrupter of claim 2 in 7 combinationwith guide means for guiding said one contact during movement thereofwhile said (two contacts are engaged, said guide means includingsurfaces slidable on each other and located within said gas-filledcapsule.

4. The vacuum-type circuit interrupter of claim 2 in combination withflexible conductive braid electrically interconnecting said one contactand said supporting structure and disposed within said gas-filledcapsule.

5. The vacuum-type circuit interrupter of claim 2 in combination withguide means for guiding said one contact during movement thereof, saidguide means including surfaces slidable on each other and located withinsaid gas-filled capsule, and flexible conductive braid electricallyinterconnecting said one contact and said supporting structure anddisposed within said gas-filled capsule.

V 6. The interrupter of claim 2 in which the gas within said capsulecomprises a monatomic gas having a high thermal conductivity incomparison to air.

7. The interrupter of claim 2 in which the gas Within said capsulecomprises helium.

8. The interrupter of c1a1m'2 in which said capsule is a self-containedassembly filled with gas to a predetermined pressure and sealed prior toits incorporation into said interrupter.

9. A vacuum-type circuit interrupter comprising means defining a vacuumchamber, a pair of separable contacts disposed within said chamber andarranged for relative 'movement into and out of engagement with eachother, supporting structure for one of said contacts disposed withinsaid chamber, means within said chamber for resilthe capsule endstructures to said supporting structure and the other of said capsuleend structures to said one contact, said compressed gas acting duringcontact-engagement to resist contact-separation, the surfaces of saidinterrupter that are exposed to the vacuum within said vacuum chamberbeing substantially free of adsorbed gases.

10. A vacuum-type circuit interrupter comprising means defining a vacuumchamber, a pair of separable contacts disposed within said chamber andarranged for'relative movement into and out of engagement with eachother, supporting structure on which one of said contacts is resilientlymounted for relative movement with respect to said supporting structure,a sealed gas-filled capsule having flexible metallic Walls disposedwithin said chamber, guide means located within said capsule forfrictionally guiding said one contact'during movement thereof relativeto said supporting structure, the walls of said' capsule flexing duringmovement of said one contact relative to said supporting structure, thesurfaces of said interrupter that are exposed to the vacuum within saidvacuum chamber being substantially free of adsorbed gases.

11. The vacuum-type circuit interrupter of claim 10 in combination withflexible conductive braid electrically interconnecting said one contactand said supporting structure and disposed within said gas-filledcapsule.

12. In the vacuum type circuit interrupter of claim 2, an additionalpair of separable contacts disposed Within said chamber, and means forresiliently mounting one contact of said additional pair comprising asecond sealed gas- .filled capsule disposed within said chamber andhaving flexible metallic walls permitting compression of the gastherewithin, said second capsule being so disposed that said gas iscompressed by contact-closing motion of said additional contacts afterinitial contact-engagement is established and acting thereafter toresist contact-separation.

iently mounting said one contact on said supporting structure comprisinga sealed gas-filled capsule; said capsule comprising a tubular metallicbellows providing flexible walls for permitting compression of the gaswithin said capsule and a pair of end structures disposedat'longitudinally-opposite ends of 'said bellows and joined in sealedrelationship to said bellows; means for causing the gas within saidcapsule to be compressed by contact-closing motion occurring afterinitial contact-engagement is established comprising fastening means forsecuring one of References Cited in the file of this patent UNITEDSTATES PATENTS" 693,416 Merrick et a1 Feb. 18, 1902 747,409 Fulton Dec.22, 1903 1,720,413 Greenwood July 9, 1929 1,783,279 Burnham Dec. 2,.1930 1,784,302 Millikan et a1. Dec. 9, 1930 1,952,184 Rankin Mar. 27,1934 2,027,064 Rozumek Jan. 7, 1936 2,356,174 Olken Aug. 22, 19442,794,885 Jennings June 4, 1957 2,863,026 Jennings Dec. 2, 19582,886,671 Steward et a1. May 12, 1959 2,908,780 Walters Oct. 13, 1959FOREIGN PATENTS 303,051 Great Britain Dec. 27, 1928 344,867 GreatBritain Mar. 10,1931 561,915 Germany Oct. 20, 1932 546,506 Belgium Apr.14, 1956 787,846-

Great Britain QDec. 18, 1947

